How is Sufism related to Islam?

Today we talk about an often asked question - what is the relatioship between Sufism and Islam? Are they the same thing or is there some difference?
Sources/Suggested Reading:
Karamustafa, Ahmet T. (2007). "Sufism: The Formative Period". Edinburgh University Press.
Knysh, Alexander (2017). "Sufism : A New History of Islamic Mysticism". Princeton University Press.
Malik, Jamal & John Hinnells (ed.) (2006). "Sufism in the West". Routledge.
Ridgeon, Lloyd (ed.) (2014). "The Cambridge Companion to Sufism". Cambridge University Press.
Van Bruinessen, Martin & Julia Day Howell (ed). (2007). "Sufism and the Modern in Islam". I.B. Tauris.
#Sufism #Islam #Mysticism